docs: def validate(cpf_number):
      """This function validates a CPF number.
  
      This function uses calculation package to calculate both digits
      and then validates the number.
  
      :param cpf_number: a CPF number to be validated.  Only numbers.
      :type cpf_number: string
      :return: Bool -- True for a valid number, False otherwise.
  
      """
  
      _cpf = compat.clear_punctuation(cpf_number)
  
      if (len(_cpf) != 11 or
         len(set(_cpf)) == 1):
          return False
  
      first_part = _cpf[:9]
      second_part = _cpf[:10]
      first_digit = _cpf[9]
      second_digit = _cpf[10]
  
      if (first_digit == calc.calculate_first_digit(first_part) and
         second_digit == calc.calculate_second_digit(second_part)):
          return True
  
      return False